Lithography methods have been frequently used for the production of fine features in various kinds of electronic devices, such as semiconductor devices and liquid crystal devices. However, as the device features are further miniaturized, having miniaturized resist patterns in lithography processes will also desirable.
In the advanced field, for example, a lithography process now allows the formation of a fine resist pattern having a line width of about 90 nm. However, finer pattern formation will be required in the future.
For attaining the formation of such a fine pattern having a line width of less than 90 nm, a first step is to develop a lithography device and a corresponding resist. Common factors to consider for developing the lithography device include shortening of the wavelengths of the light source such as an F2 laser, EUV (extreme UV light), electron beam, and X-ray, and increasing the numerical aperture (NA) of the lens.
However, the shortening of the optical wavelength may require a new and more expensive lithography device. In addition, due to an inverse relationship between the resolution and the focal depth width, even if the resolution is increased, a disadvantage occurs at high NA in which focal depth width decreases.
Recently, a method known as a liquid immersion lithography process has been reported (e.g., Non-Patent Documents 1, 2, and 3) as a lithography technology to solve such problems. In this process, a liquid such as purified water or a fluorine-based inert liquid (refractive index liquid, immersion liquid) is placed on a resist film in a predetermined thickness between a lens and the resist film. In this method, the space of the path of exposure light, which is conventionally filled with inert gas such as air or nitrogen, is replaced with a liquid having a higher refractive index (n), for example purified water, to attain high resolution without a decrease in focal depth width, similar to the use of a light source of shorter wavelength or a high NA lens, even if an optical source having the same exposure wavelength is employed.
Such liquid immersion lithography has been given considerable attention because its use allows a lens implemented in the existing device to realize the formation of a resist pattern superior in higher resolution property as well as excellent in focal depth in low costs.    (Non Patent Document 1) Journal of Vacuum Science & Technology B (J. Vac. Sci. Technol. B) (Issued country: U.S.A.), Vol. 17, No. 6, pages 3306-3309, 1999.    (Non Patent Document 2) Journal of Vacuum Science & Technology B (J. Vac. Sci. Technol. B) (Issued country: U.S.A.), Vol. 19, No. 6, pages 2353-2356, 2001.    (Non Patent Document 3) Proceedings of SPIE (Issued country: U.S.A.), Vol. 4691, pages 459-465, 2002.    (Patent Document 1) International Patent Publication No. 2004/074937